Like Emacs itself, almost every part of CIDER is configurable. The CIDER developers have tried to implement some reasonable defaults that should work for a large portion of the Clojure community, but we know that there is nothing approaching a "one size fits all" development environment and we've tried to create points of customization that can account for many different peoples' preferences. In this way, you should be able to make CIDER as comfortable as possible for you.

You can see every single customizable configuration option with the command M-x customize-group RET cider.

This section doesn't describe every possible customization that CIDER offers, but here are some of the most popular.

Basic Configuration

Disable Automatic cider-mode in clojure-mode Buffers

By default, CIDER enables cider-mode in all clojure-mode buffers after it establishes the first CIDER connection. It will also add a clojure-mode hook to enable cider-mode on newly-created clojure-mode buffers. You can override this behavior, however:

(setq cider-auto-mode nil)

Disable Symbol Confirmation

By default, CIDER prompts you for a symbol when it executes interactive commands that require a symbol (e.g. cider-doc). The default symbol will be the one at point. If you set cider-prompt-for-symbol to nil, CIDER will try the symbol at point first, and only prompt if that fails (this was the behavior in older CIDER releases).

(setq cider-prompt-for-symbol nil)

Log nREPL Communications

If you want to see all communications between CIDER and the nREPL server:

(setq nrepl-log-messages t)

CIDER will then create buffers named *nrepl-messages conn-name* for each connection.

The communication log is tremendously valuable for debugging CIDER-to-nREPL problems and we recommend you enable it when you are facing such issues.

Hide Special nREPL Buffers

If you're finding that *nrepl-connection* and *nrepl-server* buffers are cluttering up your development environment, you can suppress them from appearing in some buffer switching commands like switch-to-buffer(C-x b):

(setq nrepl-hide-special-buffers t)

If you need to make the hidden buffers appear When using switch-to-buffer, type SPC after issing the command. The hidden buffers will always be visible in list-buffers (C-x C-b).

Prefer Local Resources Over Remote Resources

To prefer local resources to remote resources (tramp) when both are available:

(setq cider-prefer-local-resources t)

Auto-Save Clojure Buffers on Load

Normally, CIDER prompts you to save a modified Clojure buffer when you type C-c C-k (cider-load-buffer). You can change this behaviour by adjusting cider-save-file-on-load.

Don't prompt and don't save:

(setq cider-save-file-on-load nil)

Just save without prompting:

(setq cider-save-file-on-load t)

Change the Result Prefix for Interactive Evaluation

Change the result prefix for interactive evaluation (not the REPL prefix). By default the prefix is =>.

(setq cider-eval-result-prefix ";; => ")

To remove the prefix altogether, just set it to the empty string ("").

Use a Local Copy of the JDK API Documentation

If you are targeting the JVM and prefer a local copy of the JDK API documentation over Oracle's official copy (e.g., for JavaSE 8), per nREPL's javadoc-info logic (accurate as of 29 Dec 2014), you can arrange your project to include the root path of the local API doc (i.e., where the index.html is located) to be included on your classpath (i.e., where the doc HTML files can be located by clojure.java.io/resource). For example, for Leiningen, with the local API path being /usr/share/doc/java/api/, put the following line in project.clj:

:dev {:resource-paths ["/usr/share/doc/java/api/"]}

or the following line in $HOME/.lein/profiles.clj:

:user {:resource-paths ["/usr/share/doc/java/api/"]}

More details can be found here.

Use a Local Copy of the Java Source Code

When an exception is thrown, e.g. when eval-ing (. clojure.lang.RT foo), a stack trace pops up. Some places of the stack trace link to Clojure files, others to Java files. By default, you can click the Clojure file links to navigate there. If you configure cider-jdk-src-paths, you can also click the Java file links to navigate there.

On Windows and macOS the JDK source code is bundled with the JDK. On Windows its typical location is C:\Program Files\Java\{jdk-version}\src.zip and on macOS its /Library/Java/JavaVirtualMachines/{jdk-version}/Contents/Home/src.zip.

On Linux distributions usually the source code is distributed as a separate package. Here's how do get the JDK 8 source on Ubuntu:

sudo apt install openjdk-8-source

The zip is installed to /usr/lib/jvm/openjdk-8/src.zip.

You can download Clojure Java source code from here.

Extract both and configure e.g. like so:

(setq cider-jdk-src-paths '("~/java/clojure-1.8.0-sources"
                            "~/java/openjvm-8-src"))

It's possible to use jar or zip files cider-jdk-src-paths, but extracting them is better since you get features like ag or dired-jump.

You can hide all nREPL middleware details from cider-browse-ns* and cider-apropos* commands by customizing the variable cider-filter-regexps. It should be a list of regexps matching the pattern of namespaces you want to filter out.

Its default value is '("^cider.nrepl" "^refactor-nrepl" "^clojure.tools.nrepl" "^nrepl"), the most commonly used middleware collections/packages.

An important thing to note is that this list of regexps is passed on to the middleware without any pre-processing. So, the regexps have to be in Clojure format (with twice the number of backslashes) and not Emacs Lisp. For example, to achieve the above effect, you could also set cider-filter-regexps to '(".*nrepl").

To customize cider-filter-regexps, you could use the Emacs customize UI, with M-x customize-variable RET cider-filter-regexps.

Or by including a similar snippet along with the other CIDER configuration.

(setq cider-filter-regexps '(".*nrepl"))

Truncate long lines in special buffers

By default contents of CIDER's special buffers such as *cider-test-report* or *cider-doc* are line truncated. You can set cider-special-mode-truncate-lines to nil to make those buffers use word wrapping instead of line truncating.

This variable should be set before loading CIDER (which means before require-ing it or autoloading it).

(setq cider-special-mode-truncate-lines nil)

Syntax highlighting

Dynamic syntax highlighting

CIDER can syntax highlight symbols that are known to be defined. By default, this is done on symbols from the clojure.core namespace, as well as macros from any namespace. If you'd like CIDER to also colorize usages of functions and variables from any namespace, do:

(setq cider-font-lock-dynamically '(macro core function var))

Here's how code looks without dynamic syntax highlighting.

Dynamic Font-lock Off

And here's how to the code looks when it's turned on.

Dynamic Font-lock On

Syntax highlighting for reader conditionals

By default CIDER will apply font-locking to unused reader conditional expressions depending on the buffer CIDER connection type.

Reader Conditionals

You can disable this behavior by adjusting cider-font-lock-reader-conditionals:

(setq cider-font-lock-reader-conditionals nil)

Customizing CIDER faces

CIDER defines a few custom faces that you might want to adjust (although normally your color theme should take care of them):

  • cider-deprecated-face - used for syntax highlighting deprecated vars
  • cider-instrumented-face - used for syntax highlighting instrumented for debugging vars
  • cider-traced-face - used for syntax highlighting traced vars
  • cider-reader-conditional-face - used for syntax highlighting inactive reader conditional branches

Configuring eldoc

  • Enable eldoc in Clojure buffers:
(add-hook 'cider-mode-hook #'eldoc-mode)

Eldoc

  • CIDER also would show the eldoc for the symbol at point. So in (map inc ...) when the cursor is over inc its eldoc would be displayed. You can turn off this behaviour by:
(setq cider-eldoc-display-for-symbol-at-point nil)
  • CIDER respects the value of eldoc-echo-area-use-multiline-p when displaying documentation in the minibuffer. You can customize this variable to change its behaviour.
eldoc-echo-area-use-multiline-p Behaviour
t Never attempt to truncate messages. Complete symbol name and function arglist or variable documentation will be displayed even if echo area must be resized to fit.
nil Messages are always truncated to fit in a single line of display in the echo area.
truncate-sym-name-if-fit or anything non-nil Symbol name may be truncated if it will enable the function arglist or documentation string to fit on a single line. Otherwise, behavior is just like t case.
  • CIDER will try to add expected function arguments based on the current context (for example for the datomic.api/q function where it will show the expected inputs of the query at point), if the variable cider-eldoc-display-context-dependent-info is non-nil:
(setq cider-eldoc-display-context-dependent-info t)

Overlays

When you evaluate code in Clojure files, the result is displayed in the buffer itself, in an overlay right after the evaluated code. If you want this overlay to be font-locked (syntax-highlighted) like Clojure code, set the following variable.

(setq cider-overlays-use-font-lock t)

You can disable overlays entirely (and display results in the echo-area at the bottom) with the cider-use-overlays variable.

(setq cider-use-overlays nil)

Specifying indentation

It is common for macros to require special indentation mechanisms. This is most common in macros that start with do, def, or with-. CIDER has some heuristics to detect these macros, but it also lets you explicitly specify how a macro should be indented.

Here's a simple example of how someone would specify the indent spec for a macro they've written (using an example in core):

(defmacro with-in-str
  "[DOCSTRING]"
  {:style/indent 1}
  [s & body]
  ...cut for brevity...)

And here's a more complex one:

(defmacro letfn
  "[DOCSTRING]"
  {:style/indent [1 [[:defn]] :form]}
  [fnspecs & body]
  ...cut for brevity...)

Don't worry if this looks intimidating. For most macros the indent spec should be either just a number, or one of the keywords :defn or :form. A full description of the spec is provided in the indent spec section of the manual.

If you don't want to use this feature, you can disable it by setting cider-dynamic-indentation to nil in your Emacs init file.

(setq cider-dynamic-indentation nil)

Minibuffer completion

Out-of-the box CIDER uses the standard completing-read Emacs mechanism. While it's not fancy it certainly gets the job done (just press TAB). There are, however, ways to improve upon the standard completion if you wish to.

icomplete

icomplete is bundled with Emacs and enhances the default minibuffer completion:

(require 'icomplete)

You can learn more about icomplete here.

ido

ido is also bundled with Emacs and offers more features than icomplete. If you are using ido, be sure to use both ido-everywhere and ido-completing-read+. You might also want to install ido-flex.

If you're fine with installing a third-party package for enhanced minibuffer completion you can't go wrong with the modern and versatile ivy.

Pretty-printing

You can configure the function used by CIDER for pretty-printing evaluation results and other data using the cider-pprint-fn option.

This can be one of three values (defaults to pprint):

Alternatively, cider-pprint-fn can be set to the namespace-qualified name of a Clojure function that takes a single argument and will pretty-print the value of said argument to *out*.

(setq cider-pprint-fn "user/my-pprint")

This function must be resolvable by CIDER at the time it is called (i.e. its containing namespace must have already been required).

CIDER will bind *print-length*, *print-level*, *print-meta*, and clojure.pprint/*print-right-margin* when calling the pretty-printing function - the function you provide is expected to respect these options.